Roofing granules with high solar reflectance, roofing materials with high solar reflectance, and the process of making the same

ABSTRACT

Roofing granules include a core having an average ultraviolet transmission of greater than sixty percent and an average near infrared reflectance of greater than sixty percent and a UV coating layer on the exterior surface. The coating provides UV opacity, while the core provides near infrared reflectance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates to roofing granules and roofing productsincluding roofing granules, such as roofing shingles, and to processesfor making such roofing granules.

2. Brief Description of the Prior Art

Asphalt shingles are conventionally used in the United States and Canadaas roofing and siding materials. Mineral surfaced asphalt shingles, suchas those described in ASTM D225 or D3462, are generally used insteep-sloped roofs to provide water-shedding function while addingaesthetically pleasing appearance to the roofs. The asphalt shingles aregenerally constructed from asphalt-saturated roofing felts and surfacedwith pigmented color granules, such as those described in U.S. Pat. No.4,717,614. Roofing granules are typically distributed over the upper orouter face of such shingles. The roofing granules, in general are formedfrom crushed and screened mineral materials, and serve to provide theshingle with durability. They protect the asphalt from the effects ofthe solar radiation, in particular from the degradative effects ofultraviolet rays, and of the environment, including wind, precipitation,pollution, and the like, and contribute to better reflection of incidentradiation. The granules moreover are typically colored, naturally orartificially by way of the application of pigments, to meet theaesthetic requirements of the user. Roofing granules typically aresubsequently coated with a binder containing one or more coloringpigments, such as suitable metal oxides.

The mineral particles typically used for making roofing granules, suchas talc, slag, limestone, granite, syenite, diabase, greystone, slate,trap rock, basalt, greenstone, andesite, porphyry, rhyolite, andgreystone, generally have low solar heat reflectance, that is, lowreflectance of near infrared radiation. Further, the pigments employedfor coloring roofing granules have usually been selected to provideshingles having an attractive appearance, with little thought to thethermal stresses encountered on shingled roofs. As a result, the coloredroofing granules themselves typically have low solar heat reflectance.

Other mineral particles, such as calcite, feldspar, quartz, white rock,plagioclase, or zeolite, may have high solar heat reflectance; however,they are less opaque to UV radiation and hence are not suitable forroofing granules. Other types of highly reflective synthetic particles,such as aluminum oxide, recycled ceramic particle, ceramic grog, orporous silica, are also less opaque to UV radiation and will not besuitable for roofing granules for asphalt-based roofing membranes.

The binder for the coating applied to color roofing granules can be asoluble alkali metal silicate that is subsequently insolubilized by heator by chemical reaction, such as by reaction between an acidic materialand the alkali metal silicate, resulting in an insoluble colored coatingon the mineral particles. For example, U.S. Pat. No. 1,898,345 to Demingdiscloses coating a granular material with a coating compositionincluding a sodium silicate, a coloring pigment, and a colloidal clay,and heating below the fusing temperature of sodium silicate, andsubsequently treating with a solution, such as a solution of calcium ormagnesium chloride, or aluminum sulphate, that will react with thesodium silicate to form an insoluble compound. Similarly, U.S. Pat. No.2,378,927 to Jewett discloses a coating composition for roofing granulesconsisting of sodium silicate, and clay or another aluminum-bearingcompound such as sodium aluminate, or cryolite or other insolublefluorides such as sodium silicofluoride, and a color pigment. Thecoating is then heat cured at a temperature above the dehydrationtemperature of the coating materials but below the fusion temperature atwhich the combination of materials fuses, thus producing a non-porous,insoluble weather-resistant cement. Roofing granules are typicallyproduced using inert mineral particles with metal-silicate binders andclays as a latent heat reactant at an elevated temperature, for example,such as those described in U.S. Pat. No. 2,981,636. The granules areemployed to provide a protective layer on asphaltic roofing materialssuch as shingles, and to add aesthetic values to a roof.

Depending on location and climate, shingled roofs can experience verychallenging environmental conditions, which tend to reduce the effectiveservice life of such roofs. One significant environmental stress is theelevated temperature experienced by roofing shingles under sunny, summerconditions, especially roofing shingles coated with dark colored roofinggranules. Although such roofs can be coated with solar reflective paintor coating material, such as a composition containing a significantamount of titanium dioxide pigment, in order to reduce such thermalstresses, this utilitarian approach will often prove to be aestheticallyundesirable, especially for residential roofs.

Asphalt shingles coated with conventional roofing granules are known tohave low solar heat reflectance, and hence will absorb solar heatespecially through the near infrared range (700 nm-2500 nm) of the solarspectrum. This phenomenon is increased as the granules covering thesurface become dark in color. For example, while white-colored asphaltshingles can have solar reflectance in the range of 25-35%, dark-coloredasphalt shingles can only have solar reflectance of 5-15%. Furthermore,except in the white or very light colors, there is typically only a verysmall amount of pigment in the conventional granule's color coating thatreflects solar radiation well. As a result, it is common to measuretemperatures as high as 77° C. on the surface of black roofing shingleson a sunny day with 21° C. ambient temperature. Absorption of solar heatmay result in elevated temperatures at the shingle's surroundings, whichcan contribute to the so-called heat-island effects and increase thecooling load to its surroundings. It is therefore advantageous to haveroofing shingles that have high solar reflectivity in order to reducethe solar heat absorption. The surface reflectivity of an asphaltshingle largely depends on the solar reflectance of the granules thatare used to cover the bitumen.

In recent years, the state of California has implemented a building coderequiring low-sloped roofs to have roof coverings with solar reflectancegreater than 70%. To achieve such high levels of solar reflectance, itis necessary to coat the roof with a reflective coating over granulatedroofing products, since the granules with current coloring technologyare not capable of achieving such high levels of solar reflectance.However, polymeric coatings applied have only a limited amount ofservice life and will require re-coat after several years of service.Also, the cost of adding such a coating on roof coverings can berelatively high.

In order to reduce the solar heat absorption, one may use light coloredroofing granules which are inherently more reflective towards the solarradiation. White pigment containing latex coatings have been proposedand evaluated by various manufacturers. However, consumers andhomeowners often prefer darker or earth tone colors for their roof. Inrecent years, there have been commercially available roofing granulesthat feature a reflective base coat (i.e., a white coat) and a partiallycoated top color coat allowing the reflective base coat to be partiallyrevealed to increase solar reflectance. Unfortunately, these granuleshave a “washed-out” color appearance due to the partially revealed whitebase coat.

Other manufacturers have also proposed the use of exterior-gradecoatings that were colored by infrared-reflective pigments for deep-tonecolors and sprayed onto the roof in the field. U.S. Patent ApplicationPublication No. 2003/0068469 A1 discloses an asphalt-based roofingmaterial comprising mat saturated with an asphalt coating and a topcoating having a top surface layer that has a solar reflectance of atleast 70%. U.S. Patent Application Publication No. 2003/0152747 A1discloses the use of granules with solar reflectance greater than 55%and hardness greater than 4 on the Moh's scale to enhance the solarreflectivity of asphalt based roofing products. However, there is nocontrol of color blends and the novel granules are typically availableonly in white or buff colors. U.S. Pat. No. 7,455,899 discloses anon-white construction surface comprising a first reflective coating anda second reflective coating with total direct solar reflectance of atleast 20%.

Also, there have been attempts in using special near-infrared-reflectivepigments in earth-tone colors to color roofing granules for increasedsolar reflectance. However, the addition of kaolin clays, which are usedto make the metal-silicate binder durable through heat curing,inevitably reduces the color strength or the color intensity of thepigment.

Colored roofing granules can also be prepared using a metal silicatebinder without adding clay and curing the binder at temperatures greaterthan the glass sintering temperature, or through a “pickling” process byapplying acid. However, these alternatives require either very hightemperatures, or the use of corrosive chemicals, and in many cases couldresult in loss of color due to pigment degradation by the acid.

In the alternative, a non-silicate binder, such as a synthetic polymericbinder, can be used to coat the inert mineral materials in order toproduce roofing granules with dark colors and high solar reflectance.However, the long-term durability and cost for polymeric coatings arenot as advantageous as the silicate binders.

Another approach is provided by solar control films that contain eitherthin layer of metal/metal oxides or dielectric layers through vacuumdeposition, and which have been commercially available for use inarchitectural glasses.

There is a continuing need for roofing materials, and especially asphaltshingles, that have improved resistance to thermal stresses whileproviding an attractive appearance, and providing good resistance to thedegradative effects of ultraviolet radiation.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides roofing granules, whichhave high near infrared or solar heat reflectance, such as at leastsixty percent, as well as high ultraviolet opacity, and roofing productssuch as shingles provided with such near infrared-reflective roofinggranules. The present invention also provides a process for preparingnear infrared-reflective roofing granules.

When used to prepare bituminous roofing products such as asphaltshingles, roofing granules according to the present invention reflectsolar heat by virtue of the near infrared-reflective cores whileblocking ultraviolet radiation to protect the underlying asphaltsubstrate in which they are embedded. Preferably, the roofing granuleshave an average particle size from about 0.1 mm to 3 mm, and morepreferably from about 0.5 mm to 1.5 mm.

The present invention employs inert mineral particles that have a highreflectance in the near infrared portion of the solar spectrum to serveas granule cores or as particulate components of such cores.

In one aspect of the present invention, the exterior surface of thecores is coated with a UV coating composition having a high opacity toultraviolet radiation and high transparency to near infrared radiationto form a coating layer on the cores to provide the roofing granules.Preferably, the UV coating composition is applied to provide a coveringeffective to confer high opacity to UV radiation. In order to achievehigh UV opacity, it is preferred that the UV coating composition beapplied to provide a coating covering at least 90 percent, and morepreferably at least 95 percent, of the surface area of the cores. Mostpreferably, the UV coating composition is applied to the surface of thecores to from a UV coating which completely covers the surface area orencapsulates of the cores.

In another aspect of the present invention, the cores themselves alsoprovide high opacity of ultraviolet radiation. In this aspect, the corescomprise an agglomerate including base particles which have low opacityto ultraviolet radiation and a binder which has high opacity toultraviolet radiation. In this aspect, the base particles have anaverage near infrared reflectance of greater than about 60 percent, andthe agglomerate binder has an average transmission in the near infraredand visible ranges of the electromagnetic spectrum of greater than about60 percent.

When a UV coating layer is employed, the UV coating layer that is formedfrom the UV coating composition preferably has an average ultraviolettransmission of less than ten percent and an average near infraredtransmission of greater than sixty percent. In this aspect, the corescan have an ultraviolet transmission of greater than sixty percent, andpreferably have a near infrared reflectance of greater than sixtypercent.

In one aspect of the present embodiment, the UV coating layer has anaverage transmission in the visible range of greater than sixty percent.

The UV coating layer can comprise a coating binder and, optionally, atleast one material dispersed in the coating binder. The ultravioletopacity of the UV coating layer can be provided by the coating binder,by the at least one material dispersed in the coating binder, or by acombination thereof. Preferably, the at least one material is anultraviolet absorber selected from the group consisting of organic orinorganic ultraviolet absorbing compounds, organic or inorganicultraviolet absorbing particles, and insoluble ultraviolet absorbingpigments.

Preferably, in one aspect of the present invention the ultravioletabsorbing inorganic particles comprise micronized titanium dioxide,micronized zinc oxide, and micronized cerium oxide. In another aspect,the insoluble ultraviolet absorbing inorganic particles comprisetitanium oxide nanoparticles, zinc oxide nanoparticles, iron oxidenanoparticles, and cerium oxide nanoparticles.

Thus, in one aspect of the present invention, the inorganic ultravioletabsorbing compounds or particles comprise nanoparticles of metal oxides.Preferably, the nanoparticles of metal oxides comprise titanium oxide,zinc oxides, iron oxides, cerium oxides, or their combination.Preferably, the nanoparticles have particle sizes sufficiently smallenough to have greater than 60% transparency in visible light spectrum.

In one aspect of the present invention, the organic ultravioletabsorbing particles preferably comprise micronized2,2′-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol].

In one aspect of the present invention, the inorganic ultravioletabsorbing compounds or particles comprise nanoparticles of metal oxides.Preferably, the nanoparticles of metal oxides comprise titanium oxide,zinc oxides, iron oxides, cerium oxides, or their combination.Preferably, the nanoparticles have particle sizes sufficiently smallenough to have greater than 60% transparency in visible light spectrum.

In another aspect, the organic ultraviolet absorbing compound ispreferably selected from the class consisting of triazines,benzotriazoles, benzophenones, vinyl-group containing amides, cinnamicacid amides, and sulfonated benzimidazoles.

In yet another aspect, the at least one organic ultraviolet absorbingcompound comprises at least one ultraviolet A absorber and at least oneultraviolet B absorber. Preferably, the at least one ultraviolet Aabsorber is selected from the group consisting of butylmethoxydibenzoylmethane,5-methyl-2-(1-methylethyl)cyclohexanol-2-aminobenzoate,bis[7,7-dimethyl-oxo-]terephthalylidene dicamphor sulfonic acid,methylene bis-benzotriazolyl tetramethylbutylphenol, Preferably, the atleast one ultraviolet B absorber is selected from the group consistingof octyl methoxycinnamate, 2-benzoyl-5-methoxyphenol, ethylhexylsalicylate, 2-cyano-3,3-diphenyl acrylic acid,3,3,5-trimethylcyclohexanol salicylate, phenylbenzimazole sulfonic acid,2-ethylhexyl-4-dimethylamino benzoate,2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, p-aminobenozic acid.

Many types of natural and synthetic inert materials have hightransmittance for ultraviolet radiation, making them unsuitable, per se,for bituminous roofing applications. Examples of such materials include,but not limited to, naturally occurring minerals such as calcite, whiterock, plagioclase, quartz, zeolite, limestone or marble; syntheticparticles such as refractory grog, crushed porcelain, alumina; silica,and silica gel. In some cases, however, these same materials have highsolar heat or near infrared reflectance, may be due to the presence ofporosity, since the presence of air/matrix interface will result inrefraction and scattering of incident radiation.

As roofing granule cores, the present invention makes use of materialsthat have high transparency to ultraviolet radiation and that otherwisewould be disfavored in preparing roofing granules for bituminous roofingproducts. In particular, such ultraviolet transparent cores are formedfrom at least one material selected from the group consisting ofcalcite, white rock, plagioclase, quartz, zeolite, limestone, marble,refractory grog, crushed porcelain, alumina, porous silica and silicagel. Suitable cores for preparing the roofing granules of the presentinvention can be prepared by comminuting and screening such materials toprovide an average size suitable for roofing granules. Preferably, thecores have an average particle size from about 0.1 millimeter to 2millimeters, and more preferably from about 0.4 mm to 1.5 mm. In somecases, the cores can comprise porous inorganic material having anaverage pore size from about 100 to 2500 nm. Preferably, the porousinorganic material comprising the cores has an average pore volume offrom about 10 to 50 percent. Alternatively, suitable cores can beprepared by comminuting suitable minerals to an average size less thanthat suitable for use in roofing granules to thus form small particles,and subsequently agglomerating these small particles to form cores.

Preferably, the agglomerated cores include voids effective to scatternear infrared radiation. In the alternative, the agglomerated core cancomprise particles having different refractive indices, or particleshaving phases, such as crystalline phases, having different refractiveindices, such that phase interfaces or particle boundaries are effectiveto scatter near infrared radiation.

A core binder can be included to provide mechanical strength to theagglomerated particles forming the cores. The core binder is preferablyselected from the group consisting of silicate, silica, phosphate,titanate, zirconate, and aluminate binders, and mixtures thereof. In oneaspect, the core binder preferably further comprises an inorganicmaterial selected from the group consisting of aluminosilicate andkaolin clay.

While it is anticipated that a substantial portion of the near infraredreflectivity of the roofing granules of the present invention will beprovided by the core and the intracore interfaces (that is, interfaceswithin the cores), such as the interfaces between particles and voids inthe granule cores, the near infrared reflectivity can be enhanced byincluding at least one near infrared-reflective material. For example,at least one near infrared-reflective material can be included in the UVcoating. Similarly, when formed from agglomerate, the cores can alsoinclude at least one near infrared-reflective material. In one presentlypreferred embodiment, the ultraviolet opacity of the agglomerated coresresults largely from the at least one near infrared-reflective materialrather than from scattering from intracore interfaces, such as theinterfaces between particles and voids. Alternatively, at least one nearinfrared-reflective material can be included in a separate coating layerapplied over the UV coating or under the UV coating. Preferably, thenear infrared-reflective material is selected from the group consistingof titanium dioxide, zinc oxide, metal pigments, titanates, and metalreflective pigments. In one presently preferred embodiment, the roofinggranules further include a near infrared-reflective coating layer.Preferably, the near infrared reflecting coating layer comprises a metalfilm.

The present invention also provides colored roofing granules. Inaddition to the effective UV resistance and near infrared reflectance,the roofing granules of the present invention can include at least onecolorant, preferably a color pigment, to provide a desired appearance inthe visible range. Preferably, at least one color pigment is dispersedin the UV coating layer. Preferably, the at least one color pigment hasan average transmission of at least sixty percent in the near infraredrange of the electromagnetic spectrum. Preferably, the at least onecolor pigment has an average ultraviolet transmission of less than tenpercent.

In addition, or in the alternative, the at least one colorant can bedispersed in a suitable binder to form a color coating composition toform a color coating layer. A color coating can be applied over the UVcoating layer or under the UV coating layer. When a nearinfrared-reflective material is employed, the at least one colorant canbe included with near infrared-reflective material in the UV coating, orin a separate coating layer over or under the UV coating.

In one aspect, roofing granules of the present invention further includeat least one biocide. The UV coating layer can include the at least onebiocide. The roofing granules of the present invention can furtherinclude an additional coating layer, the additional coating layerincluding the at least one biocide.

The UV coating composition forming the UV coating layer can include abinder preferably selected from the group consisting of metal silicate,phosphate, silica, acrylate, polyurethane, silicone, fluoropolymer andpolysilazane.

By applying a UV coating that is both opaque to ultraviolet radiationand transparent to near infrared radiation according to the presentinvention, such mineral particles are rendered suitable for roofingapplications, and yet still maintain their high near infraredreflectance properties.

In another aspect, the present invention provides a coating process forthe UV coating to encapsulate the mineral particles such that the UVcoating will cover at least 90 percent of the surface area of theparticles, and more preferably at least 95 percent of the surface areaof the particles, to provide adequate UV opacity. Most preferably, theparticles are completely encapsulated by the UV coating.

Roofing granules according to the present invention can be employed toprepare bituminous roofing products, such as shingles and roll roofingmaterial products.

In another aspect, the present invention provides a process forpreparing roofing granules. The process includes providing cores havingan average ultraviolet transmission of greater than sixty percent and anaverage solar reflectance of greater than sixty percent, the core havingan exterior surface. In one aspect, the process further includesapplying a UV coating composition on the exterior surface of the cores,and curing the UV coating composition to provide a coating on theexterior surface of the cores to form a UV coating layer. The UV coatingpreferably has an average ultraviolet transmission of less than tenpercent and an average near infrared transmission of greater than sixtypercent. In one aspect, the process further includes agglomeratingultraviolet transparent base particles to form cores. The base particlesare optionally agglomerated using a binder, and the binder can provideUV opacity to the cores. In another aspect, the process also includesproviding ultraviolet transparent mineral particle grains, and applyinga color coating to the grains to form cores. Preferably, the UV coatingis applied uniformly to the surface of the exterior surface of thecores, such as by a fluidized bed technique.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a reproduction of the results of a UV opacity test for asample of roofing granules prepared according to the prior art.

FIG. 2 is a reproduction of the results of a UV opacity test for asample of roofing granules prepared according to the present invention.

FIG. 3 is chart illustrating the results of an algae spray test for asecond sample of roofing granules prepared according to the presentinvention.

FIG. 4 is a schematic sectional elevational representation of a roofinggranule according to a first embodiment of the present invention.

FIG. 5 is a schematic sectional elevational representation of a roofinggranule according to a second embodiment of the present invention.

FIG. 6 is a schematic sectional elevational representation of a roofinggranule according to a third embodiment of the present invention.

FIG. 7 is a schematic sectional elevational representation of a roofinggranule according to a fourth embodiment of the present invention.

FIG. 8 is a schematic sectional elevational representation of a roofinggranule according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION

The present invention provides roofing granules which have high nearinfrared reflectance as well as high opacity to solar ultravioletradiation, and roofing products such as shingles provided with such nearinfrared-reflective roofing granules. The present invention alsoprovides a process for preparing these near infrared-reflective roofinggranules. Inert mineral particles are employed as cores for the roofinggranules. The inert mineral particles preferably have a high reflectancein the near infrared portion of the solar spectrum. The exterior surfaceof the cores is coated with a UV coating composition having a highopacity to ultraviolet radiation and, preferably, high transparency tonear infrared radiation, to form a coating layer on the cores.

As used in the present specification and claims, “nearinfrared-reflective,” and “solar heat-reflective” refer to reflectancein the near infrared range (700 to 2500 nanometers) of theelectromagnetic spectrum. “Visible” refers to the visible range of theelectromagnetic spectrum (400 to 700 nm). “Ultraviolet” and “UV” referto the ultraviolet range (10 to 400 nanometers) of the electromagneticspectrum. “UVA” refers to the portion of the spectrum having wavelengthsfrom 315 to 400 nanometers. “UVB” refers to the portion of the spectrumhaving wavelengths from 280 to 315 nanometers. As used in the presentspecification and claims, the “opacity” of an object or medium refers tothe extinction of incident radiation by the object or medium and is thesum of the absorption of incident radiation and the scattering ofincident radiation. As used in the present specification and claims,“about” means plus or minus five percent or less. As used in the presentspecification and claims, “encapsulate” means to cover completely, thatis, to cover 100 percent of the surface.

As used in the present specification and claims, “solar reflectivefunctional pigment” denotes a pigment selected from the group consistingof light-interference platelet pigments including mica,light-interference platelet pigments including titanium dioxide,mirrorized silica pigments based upon metal-doped silica, metal flakepigments, metal oxide coated flake pigments, and alumina. As used in thepresent specification and claims, “granule coloring pigment” denotes aconventional metal oxide-type pigment employed to color roofinggranules. As used in the present specification and claims, the strengthin color space E* is defined as E*=(L*²+a*²+b*²)^(1/2), where L*, a*,and b* are the color measurements for a given sample using the 1976 CIEL*a*b* color space. The total color difference ΔE* is defined asΔE*=(ΔL*²+Δa*²+Δb*²)^(1/2) where ΔL*, Δa*, and Δb* are respectively thedifferences in L*, a* and b* for two different color measurements.

Preferably, the present invention provides highly reflective, solid,durable, and crush-resistant granules suitable for roofing applicationswith the sizes ranging from −10 to +40 U.S. mesh.

Preferably, the solar heat reflective roofing granules according to thepresent invention have a solar reflectance of at least about 60 percent,and more preferably at least about 70 percent.

The mineral particles employed in the process of the present inventionare preferably chemically inert materials. The mineral particlespreferably have an average particle size of from about 0.1 mm to about 2mm, and more preferably from about 0.4 mm to about 1.5 mm. In someembodiments, the mineral particles employed are agglomerated particlesof smaller dimensions.

Bituminous organic materials, such as those employed in preparingwaterproof roofing shingles and roll roofing materials, are sensitive todegradation from exposure to ultraviolet radiation. Many types ofnatural and synthetic inert materials have high transmittance forultraviolet radiation, making them unsuitable or less desirable forbituminous roofing applications for this reason than other types ofinorganic materials. Examples of materials which have undesirably lowopacity to ultraviolet radiation include, but are not limited to,naturally occurring minerals such as calcite, white rock, plagioclase,quartz, zeolite, limestone or marble, and other minerals includingsubstantial proportions of silica; synthetic particles such asrefractory grog, crushed porcelain, alumina; silica, and silica gel. Insome cases, however, these same materials have desirable high solar heator near infrared reflectance. This near infrared reflectance can resultfrom porosity.

The presence of an air/matrix interface at the pores and concomitantdifference in refractive index results in refraction and scattering ofincident radiation. Depending on the physical characteristics of thepores, incident near infrared radiation can be scattered rendering theporous material opaque. To effectively scatter the incident nearinfrared radiation, the average pore size is preferably on the order ofthe wavelength of the incident near infrared radiation. Interfacesbetween materials having different refractive indices effective toscatter near infrared radiation can be provided according to the presentinvention in other ways. For example, the cores can comprise a materialhaving different phases, such as different crystalline phases or one ormore crystalline phase and an amorphous phase, each phase having adifferent refractive index, such that the scattering of incident nearinfrared radiation occurs at the interface between the phases.Alternatively, the cores can include a plurality of discrete particlesagglomerated with a binder having a refractive index different from therefractive index of the discrete particles, such that the scattering ofincident near infrared radiation occurs at the interface between thediscrete particles and the binder.

Fine particulates of the natural, manufactured, and recycled materialscan be agglomerated to provide cores having an average size suitable forroofing granules. Preferably, the agglomerated cores include nearinfrared radiation-scattering voids and/or or bound with a binder havinga refractive index differing from that of the fine particulates. Varioustypes of stone dust can be employed in the process of the presentinvention. Stone dust is a natural aggregate produced as a by-product ofquarrying, stone crushing, machining operations, and similar operations.In particular, dust from naturally occurring minerals such as calcite,white rock, plagioclase, quartz, zeolite, limestone or marble can beused, as well as manufactured or recycled manufactured materials such asrefractory grog, crushed porcelain, alumina; silica, and silica gel, andthe like. Preferably, the core-forming mineral particles aremanufactured from crushing naturally occurring rocks into suitablesizes. The cores can be prepared by comminuting and screening thematerial to provide an average size suitable for roofing granules.Preferably, the cores have an average particle size from about 0.1 mm toabout 2 mm, preferably about 0.4 mm to about 1.5 mm. Preferably, thecores comprise porous inorganic material having an average pore sizeselected to effective scatter near infrared radiation. Preferably thecores have an average pore size of from about 100 to 2500 nm.Preferably, the porous inorganic material comprising the cores has anaverage pore volume of from about 10 to 50 percent. Alternatively,suitable cores can be prepared by comminuting suitable minerals to anaverage size less than that suitable for use in roofing granules to thusform small particles, and subsequently agglomerating these smallparticles to form cores. A core binder can be included to providemechanical strength to the agglomerated particles forming cores. Thecore binder is preferably selected from the group consisting ofsilicate, silica, phosphate, titanate, zirconate, and aluminate binders,and mixtures thereof. In one aspect, the core binder preferably furthercomprises an inorganic material selected from the group consisting ofaluminosilicate and kaolin clay. Formation of the agglomerated mineralparticles into cores can be accomplished as disclosed in United StatesPatent Publication 2004/0258835 A1 incorporated herein by reference.

While it is anticipated that a substantial portion of the near infraredreflectivity of the roofing granules of one presently preferredembodiment of the present invention will be provided by the core and thevoids in the granule cores, the near infrared reflectivity of thegranules can be enhanced by including at least one nearinfrared-reflective material. For example, at least one nearinfrared-reflective material can be included in the UV coating.

Alternatively, when formed from agglomerate, the cores can include atleast one near infrared-reflective material to provide near infraredreflectivity to the cores, with scatter from interfaces such as thoseprovided by porosity making only a minor contribution to the nearinfrared reflectivity of the cores.

Examples of near infrared-reflective materials that can be employedinclude solar-reflective fillers and pigments such as rutile titaniumdioxide and anatase titanium dioxide, aluminum oxide, mullite, zincoxide, calcium carbonate, metal particles, metal flakes, ceramicparticles, refractory grog, crushed porcelain, crushed concrete,reflective polymeric particles, lithopone, zinc sulfide, white lead,metal pigments, titanates, and mirrorized silica pigments.

An example of titanium dioxide that can be employed in the solarreflective roofing granules of the present invention includes R-101which is available from Du Pont de Nemours, P.O. Box 8070, Wilmington,Del. 19880.

Examples of mirrorized silica pigments that can be employed in theprocess of the present invention include pigments such as Chrom Brite™CB4500, available from Bead Brite, 400 Oser Ave, Suite 600, Hauppauge,N.Y. 11788.

Examples of metal pigments that can be employed in the roofing granulesof the present invention include aluminum flake pigment, copper flakepigments, copper alloy flake pigments, and the like. Metal pigments areavailable, for example, from ECKART America Corporation, Painesville,Ohio 44077. Suitable aluminum flake pigments include water-dispersiblelamellar aluminum powders such as Eckart RO-100, RO-200, RO-300, RO-400,RO-500 and RO-600, non-leafing silica coated aluminum flake powders suchas Eckart STANDART PCR-212, PCR 214, PCR 501, PCR 801, and PCR 901, andSTANDART Resist 211, STANDART Resist 212, STANDART Resist 214, STANDARTResist 501 and STANDART Resist 80; silica-coated oxidation-resistantgold bronze pigments based on copper or copper-zinc alloys such asEckart DOROLAN 08/0 Pale Gold, DOROLAN 08/0 Rich Gold and DOROLAN 10/0Copper.

Examples of titanates that can be employed in the nearinfrared-reflective roofing granules of the present invention includetitanate pigments such as colored rutile, priderite, and pseudobrookitestructured pigments, including titanate pigments comprising a solidsolution of a dopant phase in a rutile lattice such as nickel titaniumyellow, chromium titanium buff, and manganese titanium brown pigments,priderite pigments such as barium nickel titanium pigment; andpseudobrookite pigments such as iron titanium brown, and iron aluminumbrown. The preparation and properties of titanate pigments are discussedin Hugh M. Smith, High Performance Pigments, Wiley-VCH, pp. 53-74(2002).

Examples of near infrared-reflective pigments available from theShepherd Color Company, Cincinnati, Ohio, include Arctic Black 10C909(chromium green-black), Black 411 (chromium iron oxide), Brown 12 (zinciron chromite), Brown 8 (iron titanium brown spinel), and Yellow 193(chrome antimony titanium).

Aluminum oxide, preferably in powdered form, can be used as nearinfrared-reflective additive to improve the solar reflectance of theroofing granules. The aluminum oxide should have particle size less than#40 mesh (425 micrometers), preferably between 0.1 micrometers and 5micrometers. More preferably, the particle size is between 0.3micrometers and 2 micrometers. The alumina should have a percentage ofaluminum oxide greater than 90 percent, more preferably greater than 95percent. Preferably the alumina is incorporated into the granule so thatit is concentrated near and/or at the outer surface of the granule.

The near infrared-reflective roofing granules of the present inventioncan also include light-interference platelet pigments.Light-interference platelet pigments are known to give rise to variousoptical effects when incorporated in coatings, including opalescence or“pearlescence.”

Examples of light-interference platelet pigments that can be employed inthe process of the present invention include pigments available fromWenzhou Pearlescent Pigments Co., Ltd., No. 9 Small East District,Wenzhou Economical and Technical Development Zone, Peoples Republic ofChina, such as Taizhu TZ5013 (mica, rutile titanium dioxide and ironoxide, golden color), TZ5012 (mica, rutile titanium dioxide and ironoxide, golden color), TZ4013 (mica and iron oxide, wine red color),TZ4012 (mica and iron oxide, red brown color), TZ4011 (mica and ironoxide, bronze color), TZ2015 (mica and rutile titanium dioxide,interference green color), TZ2014 (mica and rutile titanium dioxide,interference blue color), TZ2013 (mica and rutile titanium dioxide,interference violet color), TZ2012 (mica and rutile titanium dioxide,interference red color), TZ2011 (mica and rutile titanium dioxide,interference golden color), TZ1222 (mica and rutile titanium dioxide,silver white color), TZ1004 (mica and anatase titanium dioxide, silverwhite color), TZ4001/600 (mica and iron oxide, bronze appearance),TZ5003/600 (mica, titanium oxide and iron oxide, gold appearance),TZ1001/80 (mica and titanium dioxide, off-white appearance), TZ2001/600(mica, titanium dioxide, tin oxide, off-white/gold appearance),TZ2004/600 (mica, titanium dioxide, tin oxide, off-white/blueappearance), TZ2005/600 (mica, titanium dioxide, tin oxide,off-white/green appearance), and TZ4002/600 (mica and iron oxide, bronzeappearance).

Examples of light-interference platelet pigments that can be employed inthe process of the present invention also include pigments availablefrom Merck KGaA, Darmstadt, Germany, such as Iriodin® pearlescentpigment based on mica covered with a thin layer of titanium dioxideand/or iron oxide; Xirallic™ high chroma crystal effect pigment basedupon Al₂O₃ platelets coated with metal oxides, including Xirallic T60-10 WNT crystal silver, Xirallic T 60-20 WNT sunbeam gold, andXirallic F 60-50 WNT fireside copper; Color Stream™ multi color effectpigments based on SiO₂ platelets coated with metal oxides, includingColorStream F 20-00 WNT autumn mystery and ColorStream F 20-07 WNT violafantasy; and ultra interference pigments based on titanium dioxide andmica.

A colored, near infrared-reflective pigment can also be employed inpreparing the near infrared-reflective roofing granules of the presentinvention. Preferably, the colored, infrared-reflective pigmentcomprises a solid solution including iron oxide, such as disclosed inU.S. Pat. No. 6,174,360, incorporated herein by reference. The coloredinfrared-reflective pigment can also comprise a near infrared-reflectingcomposite pigment such as disclosed in U.S. Pat. No. 6,521,038,incorporated herein by reference. Composite pigments are composed of anear-infrared non-absorbing colorant of a chromatic or black color and awhite pigment coated with the near-infrared non-absorbing colorant.Near-infrared non-absorbing colorants that can be used in the presentinvention are organic pigments such as organic pigments including azo,anthraquinone, phthalocyanine, perinone/perylene, indigo/thioindigo,dioxazine, quinacridone, isoindolinone, isoindoline,diketopyrrolopyrrole, azomethine, and azomethine-azo functional groups.Preferred black organic pigments include organic pigments having azo,azomethine, and perylene functional groups. When organic colorants areemployed, a low temperature cure process is preferred to avoid thermaldegradation of the organic colorants.

The amount of near infrared-reflective particles added is preferablysuch that the resulting near infrared-reflective roofing granules have anear infrared reflectance of at least about 60 percent, and preferablyat least about 70 percent.

In addition to the effective UV resistance and near infraredreflectance, the roofing granules of the present invention can includeat least one colorant, preferably a color pigment, to provide a desiredappearance in the visible range. Preferably, the at least one colorpigment is dispersed in the UV coating layer.

Preferably, the at least one color pigment has an average transmissionof at least sixty percent in the near infrared range of theelectromagnetic spectrum. Preferably, the at least one color pigment hasan average ultraviolet transmission of less than ten percent.

In addition, or in the alternative, the at least one colorant, such asone or more conventional metal oxide-type granule coloring pigments, canbe dispersed in a suitable binder to form a color coating composition toform a color coating layer. A color coating can be applied over the UVcoating layer or under the UV coating layer. When a nearinfrared-reflective material is employed, the at least one colorant canbe included with near infrared-reflective material in the UV coating, orin a separate coating layer over or under the UV coating. Examples ofcoatings pigments that can be used include those provided by the ColorDivision of Ferro Corporation, 4150 East 56th St., Cleveland, Ohio44101, and produced using high temperature calcinations, includingPC-9415 Yellow, PC-9416 Yellow, PC-9158 Autumn Gold, PC-9189 BrightGolden Yellow, V-9186 Iron-Free Chestnut Brown, V-780 Black, V0797 IRBlack, V-9248 Blue, PC-9250 Bright Blue, PC-5686 Turquoise, V-13810 Red,V-12600 Camouflage Green, V12560 IR Green, V-778 IR Black, and V-799Black. Further examples of coatings pigments that can be used includewhite titanium dioxide pigments provided by Du Pont de Nemours, P.O. Box8070, Wilmington, Del. 19880.

In another aspect of the present invention, the cores are coated with atleast one thin metal layer. Preferably, the thickness of the coatingformed by the at least one metal layer is selected to maximize nearinfrared reflectivity consistent with achieving the desired color tonefor the roofing granule. The deposition of thin metal films by a varietyof techniques is well known in the art. Preferably, each of the layersof thin film is applied by an application process selected from thegroup consisting of atmospheric plasma deposition, plasma-assistedpolymerization, chemical vapor deposition, physical vapor deposition,sputtering, casting, coating, laminating, electroplating, electrolessplating, and thermal spraying. Preferably, the application process isselected from the group consisting of atmospheric plasma deposition,plasma-assisted polymerization, and physical vapor deposition.Preferably, each of the layers of the thin film comprises a materialselected from the group consisting of silver, aluminum, copper, zinc,tin, gold, palladium, nickel, and alloys thereof. Each of the layers ofthin film can comprise an alloy of silver and copper, an alloy of goldand palladium, etc.

In one aspect, roofing granules of the present invention further includeat least one biocide. The UV coating layer can include the at least onebiocide. Further, the roofing granules of the present invention canfurther include an additional coating layer, the additional coatinglayer including the at least one biocide. Suitable biocides aredisclosed, for example, in U.S. Patent Publications 2004/0255548 A1,2004/0258835 A1, 2007/0148340 A1, 2007/0148342 A1, and 2008/01186640 A1,each incorporated herein by reference.

In one aspect of the present embodiment, the UV coating layer has anaverage transmission in the visible range of greater than sixty percent.

The UV coating layer can comprise a coating binder and, optionally, atleast one material dispersed in the coating binder. The ultravioletopacity of the UV coating layer can be provided by the coating binder,the at least one material dispersed in the coating binder, or by acombination thereof. Preferably, the at least one material is anultraviolet absorber selected from the group consisting of organicultraviolet absorbing compounds, organic ultraviolet absorbingparticles, and insoluble ultraviolet absorbing pigments.

Preferably, in one aspect the ultraviolet absorbing inorganic pigmentscomprise micronized titanium dioxide, micronized zinc oxide, andmicronized cerium oxide. In another aspect, the insoluble ultravioletabsorbing inorganic particles comprise titanium oxide nanoparticles,zinc oxide nanoparticles, iron oxide nanoparticles, and cerium oxidenanoparticles.

In one aspect, the organic ultraviolet absorbing particles preferablycomprise micronized2,2′-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol].

In one aspect, the organic ultraviolet absorbing compound is preferablyselected from the class consisting of triazines, benzotriazoles,benzophenones, vinyl-group containing amides, cinnamic acid amides, andsulfonated benzimidazoles.

In another aspect, the at least one organic ultraviolet absorbingcompound comprises at least one ultraviolet A absorber and at least oneultraviolet B absorber. Preferably, the at least one ultraviolet Aabsorber is selected from the group consisting of butylmethoxydibenzoylmethane,5-methyl-2-(1-methylethyl)cyclohexanol-2-aminobenzoate,bis[7,7-dimethyl-oxo-]terephthalylidene dicamphor sulfonic acid,methylene bis-benzotriazolyl tetramethylbutylphenol, Preferably, the atleast one ultraviolet B absorber is selected from the group consistingof octyl methoxycinnamate, 2-benzoyl-5-methoxyphenol, ethylhexylsalicylate, 2-cyano-3,3-diphenyl acrylic acid,3,3,5-trimethylcyclohexanol salicylate, phenylbenzimazole sulfonic acid,2-ethylhexyl-4-dimethylamino benzoate,2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, p-aminobenozic acid.

Binders employed in the compositions of the present invention, such asbinders for UV coating compositions forming the UV coating layer, andbinders employed to form cores from agglomerated particulates, caninclude a binder preferably selected from the group consisting of metalsilicate, phosphate, silica, acrylate, polyurethane, silicone,fluoropolymer and polysilazane. Examples of suitable phosphate bindersare disclosed, for example, in International Application PCT/US08/64674,incorporated herein by reference. The UV coating compositions and/or thecore binder composition employed in the present invention can be liquidpolymeric compositions such as solutions in which a suitable polymericbinder is dissolved in an organic solvent, or aqueous polymercompositions such as aqueous dispersions of a suitable polymeric binder.Alternatively, powder coating compositions, such as a powder coatingcomposition including a suitable polymeric binder in solid form, can beemployed. Whatever the physical form of the polymeric coatingcomposition, the polymeric binder is preferably selected to provide goodUV resistance to the roofing granules of the present invention. Thus,polymeric binders with good UV resistance, such as poly(meth)acrylatebinders, are preferred. Alternatively, the binder can be a silicate-typebinder such as can be employed to prepare the agglomerated cores of thepresent invention.

The UV coating composition and the core binder compositions can alsoinclude other components, such as colorants, biocides, curing agents,viscosity modifiers, adhesion promoters, coalescing agents, film formingagents, solvents, catalysts, extenders, and fillers.

The near infrared-reflective roofing granules of the present inventioncan include conventional coatings pigments such that the coated granulesnot only have high UV opacity, but also have aesthetically pleasingcolors. Examples of coatings pigments that can be used include thoseprovided by the Color Division of Ferro Corporation, 4150 East 56th St.,Cleveland, Ohio 44101, and produced using high temperature calcinations,including PC-9415 Yellow, PC-9416 Yellow, PC-9158 Autumn Gold, PC-9189Bright Golden Yellow, V-9186 Iron-Free Chestnut Brown, V-780 Black,V0797 IR Black, V-9248 Blue, PC-9250 Bright Blue, PC-5686 Turquoise,V-13810 Red, V-12600 Camouflage Green, V12560 IR Green, V-778 IR Black,and V-799 Black. Such conventional coatings pigments can be included inthe UV coating composition, or in a separate inner coating layer formedover the mineral particles forming the cores and under the outer UVcoating layer. Preferably, the conventional color pigment chosen alsoprovides relatively high level of transparency in the near infraredportion of the electromagnetic spectrum, such that the solar heat can bepreferentially reflected by the highly reflective substrate particle.Examples of such coloring pigments are disclosed, for example, in U.S.Pat. No. 7,241,500, incorporated herein by reference. Furthermore, thecolor pigments employed preferably have high UV opacity, such that theuse of UV absorber in the UV coating can be reduced.

The present invention also provides a process for preparing nearinfrared-reflective roofing granules. The process includes providingcores preferably having an average ultraviolet transmission of greaterthan sixty percent and an average solar reflectance of greater thansixty percent. In one presently preferred embodiment of the presentinvention, a UV coating composition is applied on the exterior surfaceof the cores. In another embodiment of the process of the presentinvention, an inner coating layer is applied over the cores, and the UVcoating composition is applied to the inner coating layer to form the UVcoating layer. In one aspect, the inner coating layer provides nearinfrared reflectivity supplementing the infrared reflectivity providedby the near infrared-reflective core. Such near infrared-reflectivecoating layers can be formed from one or more metal films.Alternatively, such near infrared-reflective coating layers can beformed by including one or more near infrared-reflective materials in asuitable binder to form a near infrared-reflective coating composition.The near infrared-reflective coating composition can be applied toparticles or grains of suitable infrared-reflective minerals, andsubsequently cured to provide cores. In one aspect, the process furtherincludes agglomerating ultraviolet transparent base particles to formcores or grains.

In one aspect, the process of the present invention comprises providinga binder and inert mineral particles; dispersing the inert mineralparticles in the binder to form a mixture; optionally adding processingaids and/or other additives to the mixture; forming the mixture intouncured or “green” cores or grains; and curing the binder. The cores canbe formed by the methods disclosed in United States Patent Publication2004/0258835 A1. The “green” or uncured cores can be formed by usingrelatively low-cost raw materials, such as UV transparent stone dust,and adding water and/or a suitable binder followed by a suitablegranulation or agglomeration process to form the uncured cores. Theseraw materials can be mixed to form a mixture with suitable consistency,and then formed into particles with suitable granule size ranging frommesh #40 to mesh #8 through proper granulation process or by cementcasting. After forming the granule core, the cores can be cured eitherthrough heat treatment or chemical reaction to produce granules withenough crushing strength that is needed for the manufacturing of asphaltshingles. In another aspect, the process also includes providingultraviolet transparent mineral particle grains, and applying a colorcoating to the grains to form cores.

In particular, the core binder can be a binder selected from the groupconsisting of clay, cement, alkali metal silicates such as sodiumsilicate and potassium silicate, silicate, silica, phosphate, titanate,zirconate, and aluminate binders, and mixtures thereof. The binder canfurther comprise an inorganic material selected from the groupconsisting of aluminosilicate and kaolin clay. In one aspect of thepresent invention, the binder is a soluble alkali metal silicate, suchas aqueous sodium silicate or aqueous potassium silicate. The solublealkali metal silicate is subsequently insolubilized by heat or bychemical reaction, such as by reaction between an acidic material andthe alkali metal silicate, resulting in cured solar reflective granules.The binder may also include additives for long term outdoor durabilityand functionality.

When an alkali metal-silicate binder such as sodium silicate is employedin the preparation of solar reflective cores, the binder can include aheat-reactive aluminosilicate material, such as clay, for example,kaolin clay. Alternatively, it is possible to insolubilize the metalsilicate binder chemically by reaction with an acidic material, forexample, ammonium chloride, aluminum chloride, hydrochloric acid,calcium chloride, aluminum sulfate, and magnesium chloride, such asdisclosed in U.S. Pat. Nos. 2,591,149, 2,614,051, 2,898,232 and2,981,636, or other acidic material such as aluminum fluoride. Thebinder can also be a controlled release sparingly water soluble glasssuch as a phosphorous pentoxide glass modified with calcium fluoride,such as disclosed in U.S. Pat. No. 6,143,318. The most commonly usedbinder for conventional granule coating is a mixture of an alkali metalsilicate and an alumino-silicate clay material.

Examples of clays that can be employed in the process of the presentinvention include kaolin, other aluminosilicate clays, Dover clay,bentonite clay, etc.

The mixture of mineral particles, solar reflective particles and bindercan be formed into uncured solar reflective cores, using a formingprocess such as press, molding, cast molding, injection molding,extrusion, spray granulation, gel casting, pelletizing, compaction, oragglomeration. Preferably, the resulting uncured solar reflective coreshave sizes between about 50 micrometer and 5 mm, more preferably betweenabout 0.1 mm and 3 mm, and still more preferably between about 0.5 mmand 1.5 mm. The uncured solar reflective roofing cores can be formedusing a conventional extrusion apparatus. For example, aqueous sodiumsilicate, kaolin clay, mineral particles, and solar reflective particlesand water (to adjust mixability) can be charged to a hopper and mixed bya suitable impeller before being fed to an extrusion screw provided inthe barrel of the extrusion apparatus, such as disclosed, for example,in United States Patent Publication 2004/0258835 A1. Alternatively, theingredients can be charged to the extruder continuously by gravimetricfeeds. The screw forces the mixture through a plurality of apertureshaving a predetermined dimension suitable for sizing roofing granules.As the mixture is extruded, the extrudate is chopped by suitablerotating knives into a plurality of uncured solar reflective cores,which are subsequently fired at an elevated temperature to sinter ordensify the binder. When the formed cores are fired, such as in a rotarykiln, at an elevated temperature, such as at least 800 degrees C., andpreferably at 1,000 to 1,200 degrees C., and the binder densifies toform solid, durable, and crush-resistant cores for the granules. Inanother aspect of the present invention, near infrared-reflective coresare produced by an accretion process such as disclosed in U.S. Pat. No.7,067,445, incorporated herein by reference.

Thus, in one aspect the present invention provides roofing granulescomprising a core comprising an agglomerate comprising base particlesand an agglomerate binder. In this aspect, the base particles preferablyhave an average ultraviolet transmission of greater than about 60percent and an average near infrared reflectance of greater than about60 percent, and the agglomerate binder preferably has an averageultraviolet transmission of less than 10 percent. In this aspect, theagglomerate binder preferably has an average transmission in the nearinfrared and visible ranges of the electromagnetic spectrum of greaterthan about 60 percent.

In one aspect of the present invention, the exterior surface of thecores is coated with a UV coating composition to provide a UV coatinglayer having high opacity to ultraviolet radiation and hightransmittance for near infrared radiation. Preferably, the UV coatinglayer formed from the UV coating composition has an average ultraviolettransmission of less than ten percent and an average near infraredtransmission of greater than sixty percent. Preferably, the UV coatingis applied uniformly to encapsulate the surface of the exterior surfaceof the cores, such as by a fluidized bed technique, such as disclosed inU.S. Patent Publication 2006/0251807 A1, incorporated herein byreference, in order to ensure that the entire surface of the cores iscoated. When coating granules using conventional methods, even withmultiple conventional coats, typically only about 70% surface coveragecan be achieved. Fluidized bed coating is able to achieve a uniform andcomplete coverage of irregular surfaces, completely encapsulating thecore particles with greater than 95% surface coverage. Through use of afluidized bed encapsulation process to coat the core particles, the UVcoating composition, preferably including but not limited to pigments,binders, and UV blockers or absorbers, completely covers the entiresurface of the core particles thus achieving UV opacity, without theneed for initial coats of UV blockers or UV absorbers or multiple colorcoats.

In another aspect of the present invention the core binder compositionemployed provides UV reflectance or opacity to the cores. In this aspectof the present invention, the inert mineral particles which areagglomerated to form the cores have high UV transparency, and the UVbinder composition provides UV reflectance or UV opacity to the cores.The UV binder composition preferably includes suitable pigments,binders, and UV blockers or absorbers. Provided that the binder hassufficient UV reflectance or UV opacity so that a predetermined level ofUV opacity is achieved, a UV coating composition need not be used tocoat the surface of the core particles, or the thickness of the UVcoating layer can be reduced, and/or the concentration of UV opaquecomponent(s) of the UV coating layer can be reduced.

When used to prepare bituminous roofing products such as asphaltshingles, roofing granules according to the present invention thusreflect solar heat by virtue of the near infrared-reflective inertmineral particles while blocking ultraviolet radiation to protect theunderlying asphalt substrate in which they are embedded. Preferably, theroofing granules have an average particle size from about 0.1 mm to 3mm, and more preferably from about 0.5 mm to 1.5 mm.

The resultant granules can also be surface treated with siliconates orsuitable oils to enhance their adhesion to asphalt and also to reducetheir staining potentials.

Referring now to the drawings, in which like reference numerals refer tolike elements in each of the several views, there are shownschematically in FIGS. 4, 5, 6, 7 and 8 examples of nearinfrared-reflective roofing granules according to the present invention.

FIG. 4 is a schematic cross-sectional representation of a firstembodiment of near infrared-reflective roofing granule 10 according tothe present invention. The near infrared-reflective roofing granule 10comprises a near infrared-reflective inert mineral core particle 12coated with a UV coating layer 16 comprising UV absorptive particles 18dispersed in a UV absorptive binder 20. The presence of UV absorptiveparticles 18 can be optional provided that the UV absorptive binder 20can provide enough UV opacity. The core particles 12 have an exteriorsurface 14. A UV coating composition is applied to completely cover theexterior surface 14 of the core particles 12; and the UV coatingcomposition is cured to form the UV coating layer. Near infraredreflectance is provided to the roofing granule 10 by virtue of the nearinfrared-reflective core particles 12 by virtue of the core or aplurality of voids 22 within the core particles 12. The voids 22 arenaturally occurring defects in the mineral material comprising the coreparticles 12. The voids 22 have average dimensions on the order of thewavelength of near infrared radiation, and thus scatter incidentradiation at near infrared wavelengths, by virtue of the difference inrefractive index between the voids 22 and the core particle material.While the near infrared-reflective roofing granule 10 is shownschematically as a sphere in FIG. 4, near infrared-reflective roofinggranules according to the present invention can assume any regular orirregular shape. The particle size of the near infrared-reflectiveroofing granule 10 preferably ranges from about 0.1 mm to 3 mm, and morepreferably from about 0.5 mm to 1.5 mm.

FIG. 5 is a schematic cross-sectional representation of a secondembodiment of near infrared-reflective roofing granules 30 according tothe present invention. The near infrared-reflective roofing granules 30comprise a near infrared-reflective inert mineral core particle 32coated with a UV coating layer 36 comprising a UV absorptive binder 40.The core particles 32 have an exterior surface 34. A UV coatingcomposition is applied to completely cover the exterior surface 34 ofthe core particles 32; and the UV coating composition is cured to formthe UV coating layer. Near infrared reflectance is provided to theroofing granule 30 by virtue of the near infrared-reflective coreparticles 32 by virtue of the core or a plurality of voids 42 within thecore particles 32. The voids 42 are naturally occurring defects in themineral material comprising the core particles 32. The voids 42 haveaverage dimensions on the order of the wavelength of near infraredradiation, and thus scatter incident radiation at near infraredwavelengths, by virtue of the difference in refractive index between thevoids 42 and the core particle material.

FIG. 6 is a schematic cross-sectional representation of a thirdembodiment of near infrared-reflective roofing granule 50 according tothe present invention. The near infrared-reflective roofing granule 50comprises a near infrared-reflective inert mineral core particle 52coated with a UV coating layer 56 comprising a UV absorptive inorganicpigment such as titanium dioxide nanoparticles 58 dispersed in asuitable binder 60. The inert mineral core particle 52 has an exteriorsurface 54 to which a UV opaque coating composition is applied and curedto form the UV coating layer. The core particles 52 are formed from aplurality of agglomerated mineral particles 70 adhered together with asuitable binder material 72 and have a plurality of pores or voids 74extending throughout the core particles 52. The binder material 72 ispreferably selected from the group consisting of silicate, silica,phosphate, titanate, zirconate and aluminate binders, and mixturesthereof. The binder content of the core particles 52 preferably rangesfrom 10% to 90% by weight. The core particles 52 can be formed byextrusion, agglomeration, roll compaction, accretion, or other formingtechniques. After formation, depending on binder chemistry, the coreparticles 52 can be fired at 250 degrees C. or higher, preferably from500 degrees C. to 800 degrees C., to insolubilize the binder material72. Near infrared reflectance is provided to the roofing granules 50 byvirtue of the near infrared-reflective core particles 52 by virtue ofthe plurality of voids 74 within the core particles 52. The voids 74have average dimensions on the order of the wavelength of near infraredradiation, and thus scatter incident radiation at near infraredwavelengths.

FIG. 7 is a schematic cross-sectional representation of a fourthembodiment of near infrared-reflective roofing granule 80 according tothe present invention. The near infrared-reflective roofing granule 80comprises a near infrared-reflective inert mineral core particles 82coated with a UV coating layer 86 comprising and UV absorptive particles88 such as nano zinc oxide dispersed in a UV absorptive binder 90. Thecore particles 82 each comprise a particle or grain 100 of an inert UVtransparent mineral, such as calcite, white rock, plagioclase, quartz,zeolite, limestone, marble, refractory grog, crushed porcelain, alumina,porous silica or silica gel, coated with a near infrared-reflectivelayer 104 of a thin metal film. The inert mineral grains 100 themselvesinclude voids 102 effective to scatter incident near infrared radiation,and the near infrared-reflective layer 104 supplements the effect of thevoids 102 with respect to incident near infrared radiation. The nearinfrared-reflective film 104 is formed on the grains 100 by a metalsputtering technique.

FIG. 8 is a schematic cross-sectional representation of a fifthembodiment of near infrared-reflective roofing granules 110 according tothe present invention. The near infrared-reflective roofing granule 110comprises a near infrared-reflective inert mineral core particles 112coated with a UV coating layer 116 comprising and UV absorptive binder118 in which are dispersed metal oxide pigment particles 120 to impart adesired color to the roofing granules 100. The near infrared-reflectivecore particle 112 has an exterior surface 114 to which a UV coatingcomposition is applied and cured to form the UV coating layer 116. Thenear infrared-reflective core particle 112 comprises a inner inertmineral grain or particle 130 and an inner coating layer 140 comprisinga inner coating binder 142 in which are dispersed additional nearinfrared-reflective particles 144. Near infrared reflectance is providedto the roofing granule 110 by virtue of the near infrared-reflectivegrain 130 by virtue of a plurality of voids 132 within the grain 130.The voids 132 are naturally occurring defects in the mineral materialcomprising the grain 130. The voids 132 have average dimensions on theorder of the wavelengths of near infrared radiation, and thus scatterincident radiation at near infrared wavelengths. The grains 130 areminute particulates or dust, such as for example, particulates ofcalcite, white rock, plagioclase, quartz, zeolite, limestone, marble,refractory grog, crushed porcelain, alumina, porous silica, silica gelor other UV transparent rock sources formed as a byproduct from quarry,crushing and similar operations. The near infrared reflectance of thegrain 130 is supplemented by the near infrared-reflectance of the innercoating layer 140 by virtue of the additional near infrared-reflectiveparticles 144.

The near infrared-reflective roofing granules of the present inventioncan be employed in the manufacture of roofing products, such as asphaltshingles and bituminous membranes, using conventional roofing productionprocesses. Typically, bituminous roofing products are sheet goods thatinclude a non-woven base or scrim formed of a fibrous material, such asa glass fiber scrim. The base is coated with one or more layers of abituminous material such as asphalt to provide water and weatherresistance to the roofing product. One side of the roofing product istypically coated with mineral granules to provide durability, reflectheat and solar radiation, and to protect the bituminous binder fromenvironmental degradation. The near infrared-reflective roofing granulesof the present invention can be mixed with conventional roofinggranules, and the granule mixture can be embedded in the surface of suchbituminous roofing products using conventional methods. Alternatively,the near infrared-reflective roofing granules of the present inventioncan be substituted for conventional roofing granules in manufacture ofbituminous roofing products.

Bituminous roofing products are typically manufactured in continuousprocesses in which a continuous substrate sheet of a fibrous materialsuch as a continuous felt sheet or glass fiber mat is immersed in a bathof hot, fluid bituminous coating material so that the bituminousmaterial saturates the substrate sheet and coats at least one side ofthe substrate. The reverse side of the substrate sheet can be coatedwith an anti-stick material such as a suitable mineral powder or a finesand. Alternatively, the reverse side of the substrate sheet can becoated with an adhesive material, such as a layer of a suitablebituminous material, to render the sheet self-adhering. In this case theadhesive layer is preferably covered with a suitable release sheet.

Roofing granules are then distributed over selected portions of the topof the sheet, and the bituminous material serves as an adhesive to bindthe roofing granules to the sheet when the bituminous material hascooled.

Optionally, the sheet can then be cut into conventional shingle sizesand shapes (such as one foot by three feet rectangles), slots can be cutin the shingles to provide a plurality of “tabs” for ease ofinstallation, additional bituminous adhesive can be applied in strategiclocations and covered with release paper to provide for securingsuccessive courses of shingles during roof installation and/or aestheticeffect, and the finished shingles can be packaged. More complex methodsof shingle construction can also be employed, such as building upmultiple layers of sheet in selected portions of the shingle to providean enhanced visual appearance, or to simulate other types of roofingproducts.

In addition, the roofing membrane can be formed into roll goods forcommercial or industrial roofing applications.

Examples of suitable bituminous membranes for use in the process of thepresent invention include asphalt roofing membranes such asasphalt-based, self-adhering roofing base sheet available fromCertainTeed Corporation, Valley Forge, Pa., for example, WinterGuard™shingle underlayment, a base sheet which is impregnated with rubberizedasphalt.

Preferably, the reinforcement material comprises a non-woven web offibers. Preferably, the nonwoven web comprises fibers selected from thegroup of glass fibers, polymeric fibers and combinations thereof.Examples of suitable reinforcement material include, but are not limitedto, non-woven glass fiber mats, non-woven polyester mats, compositenon-woven mats of various fibers, composite woven fabrics of variousfibers, industrial fabrics such as papermaker's forming fabrics andpapermaker's canvasses, polymer netting, screen, and mineral particles.The fibers employed in preparing the reinforcing material can be spun,blown or formed by other processes known in the art. Yarn for formingthe reinforcement material can include mono-filament yarn,multi-filament yarn, spun yarn, processed yarn, textured yarn, bulkedyarn, stretched yarn, crimped yarn, chenille yarn, and combinationsthereof. The cross-section of the yarn employed can be circular, oval,rectangular, square, or star-shaped. The yarn can be solid, or hollow.The yarn can be formed from natural fibers such as wool and cotton;synthetic materials such as polyester, nylon, polypropylene,polyvinylidene fluoride, ethylene tetrafluoroethylene copolymer,polyethylene terephthalate, polybutylene terephthalate, polytrimethyleneterephthalate, poly(meth)acrylates, aramide, polyetherketone,polyethylene naphthalate, and the like, as well as non-organic materialssuch as spun glass fibers and metallic materials, or combinationsthereof.

Non-woven glass fiber mats for use in the process of the presentinvention preferably have a weight per unit area of from about 40 to 150g/m², more preferably form about 70 to 120 g/m², and still morepreferably from about 80 to 100 g/m², and a thickness of from about 0.01to 1 mm. Non-woven glass mats having a weight per unit area of about 90g/m² (0.018 lb/ft²) are typically employed. The bituminous material usedin manufacturing roofing products according to the present invention isderived from a petroleum-processing by-product such as pitch,“straight-run” bitumen, or “blown” bitumen. The bituminous material canbe modified with extender materials such as oils, petroleum extracts,and/or petroleum residues. The bituminous material can include variousmodifying ingredients such as polymeric materials, such as SBS(styrene-butadiene-styrene) block copolymers, resins, flame-retardantmaterials, oils, stabilizing materials, anti-static compounds, and thelike. Preferably, the total amount by weight of such modifyingingredients is not more than about 15 percent of the total weight of thebituminous material. The bituminous material can also include amorphouspolyolefins, up to about 25 percent by weight. Examples of suitableamorphous polyolefins include atactic polypropylene, ethylene-propylenerubber, etc. Preferably, the amorphous polyolefins employed have asoftening point of from about 130 degrees C. to about 160 degrees C. Thebituminous composition can also include a suitable filler, such ascalcium carbonate, talc, carbon black, stone dust, or fly ash,preferably in an amount from about 10 percent to 70 percent by weight ofthe bituminous composite material.

The following examples are provided to better disclose and teachprocesses and compositions of the present invention. They are forillustrative purposes only, and it must be acknowledged that minorvariations and changes can be made without materially affecting thespirit and scope of the invention as recited in the claims that follow.

COMPARATIVE EXAMPLE 1

Aluminum oxides known as ceramic grog (grade 90A commercially availablefrom Maryland Refractory Inc., Irondale, Ohio) are used as coreparticles. The core particles have particle sizes between US #12 meshand US #40 mesh and an initial color of L*=85.82, a*=˜0.18, b*=3.66 asmeasured by colorimeter (HunterLab Labscan XE) and a solar reflectanceof 69.0% as measured according to ASTM C-1549 procedure. The coreparticles have relatively low UV opacity of <5% as determined by the UVOpacity test listed in ARMA Granule Test Manual as Test Method #9,except that the test results were digitized by a CCD camera instead ofrecording on a photo paper. The UV test results are shown in FIG. 1. Thepresence of a spot indicates UV transparency of the granule. Due to thehigh UV transparency of this type of material, the material is deemed asnot suitable for roofing applications.

Example 1

The base particles of Comparative Example 1 were coated by a coatingcontaining nano zinc oxide and titanium dioxide as a UV blocker torender them UV opaque. This was achieved by coating 500 g of the coreparticles with a coating consisting of 32.40 g sodium silicate (grade 42from Oxychem Corp., Dallas, Tex.). 50.40 g of water, 7.20 g of kaolinclay (Unimin Corp. Hephzibah, Ga.), 10.80 g of zinc oxide (Kadox 920from Zinc Corp of America), and 6.10 g of titanium dioxide (R101 fromDuPont Corp., Wilmington, Del.). The coating was prepared by mixing theingredients in a mixer at 300 rpm until a uniform mixture and the baseparticles were then coated by the coating by using a fluidized bedcoater (model 0002 from Fluid Air Inc., Aurora, Ill.). The resultantparticles have a color reading of L*=76.34, a*=1.11, b*=5.18, and asolar reflectance of 57.1%. The UV opacity test shows that the resultantparticles have much higher UV opacity at >98% as determined by the sametest method. The result is shown in FIG. 2.

COMPARATIVE EXAMPLE 2

600 grams of grey roofing granules were prepared by coating mineralparticles having sizes between US mesh #10 and US mesh #4 with a greycoating composition composed of 125 g. sodium silicate, 21.77 grams IRtransparent and IR opaque pigments, which are as follows: 4.85 gramsSheppard 411 Black, 8.64 grams Ferro RD-1563, 0.60 grams Ferro AcidResistant Ultramarine Blue, 4.68 grams DuPont R101 TiO₂, 3.84 gramsFerro 10550 Brown, and 1.44 grams Ferro V-10411 Yellow, 18.50 grams zincoxide (Kadox 920 from Zinc Corp of America), 9.55 grams Wilky clay(available from Wilkinson Kaolin Associates, Ltd., Gordon, Ga.), and 45grams water. The coating was deposited on the mineral particles using aWurster fluidized bed coater. The grey coated granules were then curedin a rotary dryer at 565° C. (1050° F.). Finished granules were thenapplied to two panels of filled asphalt coating where a spray algae testwas conducted for 14 days. These roofing granules exhibited algaeresistance. As shown in FIG. 3, after 14 days both panels of greyroofing granules had little or no algae remaining on the panel.

Example 2

600 grams of grey roofing granules can be prepared by coating ceramicgrog 90A (a UV transparent mineral material) supplied by MarylandRefractories with a grey coating composition composed of 125 g. sodiumsilicate, 21.77 grams IR transparent and IR opaque pigments, which areas follows: 4.85 grams Sheppard 411 Black, 8.64 grams Ferro RD-1563,0.60 grams Ferro Acid Resistant Ultramarine Blue, 4.68 grams DuPont R101TiO₂, 3.84 grams Ferro 10550 Brown, and 1.44 grams Ferro V-10411 Yellow,18.50 grams zinc oxide (Kadox 920 from Zinc Corp of America), 9.55 gramsWilky clay (available from Wilkinson Kaolin Associates, Ltd., Gordon,Ga.), and 45 grams water. The coating can be deposited on the mineralparticles using a Wurster fluidized bed coater. The grey coated granulescan then be cured in a rotary dryer at 565° C. (1050° F.). Due to theopaque nature of the coating, the coated UV transparent ceramic grogmineral particle would become granules opaque to UV. Further, due to thepresence of zinc oxide, the resulting granules would also be algaeresistant. The algae resistance is expected to by similar to the algaeresistance of the granules of Comparative Example 2 because the coatingprovides the algae resistance, and not the core of the granule, assumingthe UV transparent ceramic grog core is entirely encapsulated.

Various modifications can be made in the details of the variousembodiments of the processes, compositions and articles of the presentinvention, all within the scope and spirit of the invention and definedby the appended claims.

1. Roofing granules comprising: (a) a core having an average ultraviolettransmission of greater than sixty percent and an average near infraredreflectance of greater than sixty percent, the core having an exteriorsurface, and (b) a UV coating layer to cover the exterior surface, theUV coating layer having an average ultraviolet transmission of less thanten percent and an average transmission in the near infrared and visibleranges of the electromagnetic spectrum of greater than sixty percent. 2.Roofing granules according to claim 1 wherein the UV coating layercomprises a binder and at least one material dispersed in the binder. 3.Roofing granules according to claim 2 wherein the binder has an averageultraviolet transmission of less than ten percent.
 4. Roofing granulesaccording to claim 2 wherein the at least one material comprises anultraviolet absorber selected from the group consisting of organic orinorganic ultraviolet absorbing compounds, organic or inorganicultraviolet absorbing particles, and insoluble ultraviolet absorbinginorganic pigments.
 5. Roofing granules according to claim 4 wherein theinsoluble ultraviolet absorbing inorganic pigments comprise micronizedtitanium dioxide, micronized zinc oxide, micronized iron oxide, andmicronized cerium oxide.
 6. Roofing granules according to claim 4wherein the insoluble ultraviolet absorbing inorganic particles comprisetitanium oxide nanoparticles, zinc oxide nanoparticles, iron oxidenanoparticles and cerium oxide nanoparticles.
 7. Roofing granulesaccording to claim 4 wherein the organic ultraviolet absorbing particlescomprise micronized2,2′-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol].8. Roofing granules according to claim 4 wherein the organic ultravioletabsorbing compound is selected from the class consisting of triazines,benzotriazoles, benzophenones, vinyl-group containing amides, cinnamicacid amides, diphenyl acrylates, and sulfonated benzimidazoles. 9.Roofing granules according to claim 4 wherein the organic ultravioletabsorbing compound comprises at least one ultraviolet A absorber and atleast one ultraviolet B absorber.
 10. Roofing granules according toclaim 9 wherein the at least one ultraviolet A absorber is selected fromthe group consisting of butyl methoxydibenzoylmethane,5-methyl-2-(1-methylethyl)cyclohexanol-2-aminobenzoate,bis[7,7-dimethyl-oxo-]terephthalylidene dicamphor sulfonic acid,methylene bis-benzotriazolyl tetramethylbutylphenol.
 11. Roofinggranules according to claim 9 wherein the at least one ultraviolet Babsorber is selected from the group consisting of octylmethoxycinnamate, 2-benzoyl-5-methoxyphenol, ethylhexyl salicylate,2-cyano-3,3-diphenyl acrylic acid, 3,3,5-trimethylcyclohexanolsalicylate, phenylbenzimazole sulfonic acid,2-ethylhexyl-4-dimethylamino benzoate,2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, p-aminobenozic acid.12. Roofing granules according to claim 2, the binder being selectedfrom the group consisting of metal silicate, phosphate, silica,acrylate, polyurethane, silicone, fluoropolymer and polysilazane. 13.Roofing granules according to claim 1 wherein the UV coating layerfurther comprises at least one color pigment.
 14. Roofing granulesaccording to claim 13 wherein the at least one color pigment has anaverage transmission of at least sixty percent in the near infraredrange of the electromagnetic spectrum.
 15. Roofing granules according toclaim 13 wherein the at least one color pigment has an averageultraviolet transmission of less than ten percent.
 16. Roofing granulesaccording to claim 1, the UV coating layer further comprising at leastone biocide.
 17. Roofing granules according to claim 1, the granulesfurther including an additional coating layer, the additional coatinglayer including at least one biocide.
 18. Roofing granules according toclaim 1, the granules further including a near infrared-reflectivecoating layer.
 19. Roofing granules according to claim 18, the nearinfrared coating layer comprising a metal film.
 20. Roofing granulesaccording to claim 1, the granules comprising an ultraviolet transparentcore formed from at least one material selected from the groupconsisting of calcite, plagioclase, quartz, zeolite, limestone, marble,refractory grog, crushed porcelain, alumina, porous silica and silicagel.
 21. Roofing granules according to claim 20 wherein each corecomprises agglomerate.
 22. Roofing granules according to claim 21, theagglomerate comprising base particles and an agglomerate binder. 23.Roofing granules according to claim 21, the agglomerate including nearinfrared radiation-scattering voids.
 24. Roofing granules according toclaim 21, the agglomerate further comprising at least one additionalnear infrared-reflective material.
 25. Roofing granules according toclaim 1 wherein the core comprises porous inorganic material having anaverage pore size from about 100 to 2500 nm.
 26. Roofing granulesaccording to claim 25 wherein the porous inorganic material has anaverage pore volume of from about 10 to 50 percent.
 27. Roofing granulesaccording to claim 1 wherein the UV coating layer covers at least 90percent of the surface area of the core.
 28. Roofing granules accordingto claim 27 wherein the UV coating layer covers at least 95 percent ofthe surface area of the core.
 29. Roofing granules according to claim 28wherein the UV coating layer encapsulates the core.
 30. Roofing shinglescomprising roofing granules according to claim
 1. 31. Roll roofingmaterial comprising roofing granules according to claim
 1. 32. A processfor preparing roofing granules, the process comprising: (a) providingcores having an average ultraviolet transmission of greater than sixtypercent and an average solar reflectance of greater than sixty percent,the core having an exterior surface; (b) applying a UV coatingcomposition on the exterior surface of the cores; (c) curing the UVcoating composition to provide a coating on the exterior surface of thecores to form a UV coating layer, the UV coating having an averageultraviolet transmission of less than ten percent and an average nearinfrared transmission of greater than sixty percent.
 33. A processaccording to claim 32 further comprising agglomerating ultraviolettransparent base particles to form cores.
 34. A process according toclaim 33 further comprising providing ultraviolet transparent grains,and applying a color coating to the grains to form cores.
 35. A processaccording to claim 32, wherein the UV coating is applied uniformly tothe surface of the exterior surface of the cores by a fluidized bedtechnique.
 36. A roofing granule comprising a core comprising anagglomerate comprising base particles and an agglomerate binder, thebase particles having an average ultraviolet transmission of greaterthan about 60 percent and an average near infrared reflectance ofgreater than about 60 percent, and the agglomerate binder having anaverage ultraviolet transmission of less than 10 percent and an averagetransmission in the near infrared and visible ranges of theelectromagnetic spectrum of greater than about 60 percent.